Inductive power coupling allows energy to be transferred from a power supply to an electric load without connecting wires. A power supply is wired to a primary coil and an oscillating electric potential is applied across the primary coil which induces an oscillating magnetic field. The oscillating magnetic field may induce an oscillating electrical current in a secondary coil, placed close to the primary coil. In this way, electrical energy may be transmitted from the primary coil to the secondary coil by electromagnetic induction without the two coils being conductively connected. When electrical energy is transferred from a primary coil to a secondary coil the pair are said to be inductively coupled. An electric load wired across such a secondary coil may draw energy from the power source when the secondary coil is inductively coupled to the primary coil.
The efficiency of energy transfer via an inductive coupling is greatly improved when the primary coil is well aligned with the secondary coil and the gap between the coils is minimal. Thus in transformers or other fixed inductive couplings the two coils are often wound about each other. This is not practical, however in systems where the coupling is of a temporary nature, and the secondary coil is required to be easily separated from the primary coil.
Alignment systems for inductive couplings for mobile devices include for example, the system described in U.S. Pat. No. 7,210,940 to Baily et al., which describes an inductive coupling for transferring electrical energy to or from a transducer and measuring circuit. Baily's system consists of a male connector having a single layer solenoid wound onto a ferromagnetic rod and a female connector having a second, single layer solenoid. By inserting the male connector into the female connector, the two solenoids are brought into alignment, enabling inductive energy transfer between them. This coupling provides a sealed signal connection without the disadvantages of having exposed contact surfaces.
Baily's system allows an electrical device wired to a male connector to be moved independently from a power source wired to a female connector, yet the pair may be coupled very precisely by plugging the two together. However the plugging itself may unduly restrict the freedom of movement of the electrical device which cannot move beyond the length of the connecting lead. Moreover, trailing leads are unsightly and may become snagged or tangled.
Other electrical power transmission systems have been proposed that allow a power receiving electrical device to be placed anywhere upon an extended base unit covering a larger area, thereby providing freedom of movement without requiring the trailing wires inherent in Baily. One such example is described in U.S. Pat. No. 7,164,255 to Hui. In Hui's system a planar inductive battery charging system is designed to enable electronic devices to be recharged. The system includes a planar charging module having a charging surface on which a device to be recharged is placed. Within the charging module, and parallel to the charging surface, is at least one, and preferably an array of primary windings that couple energy inductively to a secondary winding within the device to be recharged. Hui's system also provides secondary modules that allow the system to be used with conventional electronic devices not supplied with secondary windings.
Such systems typically provide a relatively low power inductive coupling which may be adequate for charging batteries. It will be appreciated however, that extended base units such as Hui's charging surface which transmit energy approximately uniformly over the whole area of the unit, are not suitable for use with high energy systems.
There is a need for a flexible inductive power transmission surface which allows relatively high power to be cordlessly provided to electrical devices positioned by a user anywhere over an extended region. The present disclosure addresses this need.